Pivot



FRED LEE, OF COVENTRY, ENGLAND.

PIVOT.

Application led May 31, 1917'.

To all whom. t may concern.' Be it known that I, FRED LEE, a sub] ect of 'the King of England, residing at Coventry, Warwickshire, England, have invented certain new and useful Improvements in Pivots, of which the following is a specilication. y

This invention relates to the pivoting of instruments and more yespecially instruments exposed to vibration, suchV for example as Compasses employed on aircraft, in which position they are subjected to exceptional vibration. The invention is, however, applicable to a variety of other instruments which are subject to vibration, for example instruments in which steel, iridium,

i or other metallic pivot points are employed.

Considerable difiiculty has arisen in connection with the -pivoting of Compasses for use on aeroplanes, in which steel, and subsequently iridium, pivot points of the wellknown kind have been employed working in a` stone cup or bearing. The vibrations of the aircraft are found to affect the working of these metal pivots andstone bearings, so that the results are unsatisfactory after a brief period of use. The point of the pivot and the stone bearing are found to be very rapidly destroyed by the vibration set up, and consequently the compass loses its sensitivity. IV ith steel pivots which have been inost usually employed workingin a stone eup under such conditions, cutting is found to occur rapidly and iridium pivot pins have given but little better success. It is the object of the present invention to overcome this difficulty.

According to this invention, in instruments subject to vibration there is employed ya pivot and a-bearing therefor, for example a cup, both of stone, such las is used for jeweled bearings, of the rubbing-surfaces being such that no roughness is visible under a magnification of not less than 25 diameters. The stone is such as is used 4for jeweled bearings to prevent deformation, sue-h as sapphire, agate, ruby, or diamond, other stones, including which are sufficiently hard to provide a good dura-ble point and to take the requisite polish, without being so hard as to be unworkable. e

The shape of the pivot is preferably that of a cone, the angle at whose apex lies between 56 and 7 0, and of` which about twosynthetic stones,

Specification of Letters Patent.

lof the pivot and cu'p.

characterized by the polishor any of the precious or,

Patented Feb. 17, 192e.

Serial No. 171,946.

thousandths of an inch at the apex have been rounded off, the side of the cone being very slightly bulged so asl to be in the form of a parabola instead of straight, whereby any tendency to crack is prevented. The choice of angle between the above limits depends upon the question whethery sensitivity or durability is more important: for durability the blunter angle is to be preferred.

One form of pivot point and cup for use in an instrument subjectto vibration, according to this invention, will now be described with reference tothe accompanying drawing which shows a much enlarged view A is the pivot of agate having an angle at its apex of between 56o and 70, and slightly blunt by having about two-thousandths of an inch at-the apex rounded off. The side of the conicalshaped point is bulged slightly so as to be in the form of a parabola. The pivot is carried in the end of a. support B of -brass or other imlterialwliich is drilled to receive it. and works in the cup C of sapphire. The rubbing surfaces of the pivot point and the cup are polished to a much higher degree than has heretofore been the practice, namely, so tha-t when exa-mined under a microscope and magnified to not less than diameters, no pits or excrescences can be seen. The cup is of suc-h curvature that the pivot will work smoothly in it and permit the tilting of the pivot when necessary.

In many cases the pivot point is carried in a hole drilled in one end of a. brass pillar which is provided at. the other end with a screw by which it is secured to the bottom of the compass case. The cup is arranged to ride on the pin.

Any form of mounting may be employed that is desirable and appropriate to the work in hand, and the pivot point and cup according to the present invention` may be employed not 'only in Compasses but in an)v kind of instrument subject to vibration for which it is suitable or desirable.

The pivot may be either stationary or rotating.

I have found this work, but from Cashmere,

Sapphires rto be suitable for of the Sapphires obtainable Ceylon, Montana and Anstralia, I have found the last mentioned used as pivot points to work satisfactorily in cups formed from Montana sapphires.

IVhen agate is employed for the pivot points, care must be taken to use only samples of the stone which are free from definite crystalline structure, and it has been found that smoky agate having an amorphous structure is most suitable, and the banded variety should not be used.

It is to be understood that thisA invention is not limited to the use of any particular stones, but consists in the employment of stone pivot pointsand stone cups in instruments subject `to vibration, such as compasses, and in affording the rubbing surfaces of the pivot point and the cup a very high degree of polish whereby they work sweetly, even though subjected to vibration, without cutting.

It has been proposed to employ in watchwork a staff having jewel pivots working in jewel holesyy-ithend-stones, and no claim is made for such construction in the present specification.

What claim as my invention and desire to secure by Letters Patent; isz

1. ln an instrument bearing the combination of a conoidal pivot, the angle at the between 56o to 70o and having about two-thousandths of an inch at the apex rounded off, and a cup-bearing thereforboth said parts being formed of stone,

such as is used for jeweled bearings, but having the rubbing surfaces polished to such a degree that roughness, if any is present, is only visible under a microscopie magnification of twenty-five diameters, or more.

Q. In an instrument bearing the combination of a. conoidal pivot the angle' at the apex being between 56C to 7.00 and having about two-thousandths of an inch at the apex rounded off, the .side of the cone being slightly bulged so as to be in the form of a parabola, `instead of straight, whereby the tendency to cracking' is prevented, and a cup bearing therefor both said parts being formed of stone, such as is used for jeweled bearings, but having the rubbing surfaces polished to such a -degree that roughness, if

l any is presenjis only visible under amicroscropic magnification of twenty-five diameters, or more.

In testimony whereof I have signed my name to this specification in the presence of two subscribing Witnesses.

FRED LEE.

lVitnesses:

HAROLD H. SIMMONS, HARRY S. WENDEY. 

